There are a great many circuits of the capacitive type which are operated by the approach of a body toward or to an antenna probe to thereby actuate the control circuit from one state to another state. A high degree of sensitivity is easily attained, but most of the prior art circuits suffer from poor stability, thereby tending to render them less than satisfactory as continuously-operating control circuits. Shaping of the input signals is frequently resorted to in order to increase the stability, such shapings taking various forms.
U.S. Pat. No. 3,811,054 to Wern et al shows the broad idea of a probe controlling a triac, which in turn is kept alive by locally generated oscillator pulses. U.S. Pat. No. 4,037,221 to Alexander is of a similar type and shows some degree of shaping of the input signal from the probe including amplifiers and an integrator which integrates a portion of the incoming signals from the touch plate probe.
U.S. Pat. Nos. 3,770,981 to Nelsen; 3,965,465 to Alexander and 4,031,408 to Holz show the idea of adjusting the sensitivity of the incoming signal from the probe, and in the latter patent CMOS circuitry is used. However, the problems involved in using CMOS circuitry as a detector are met in a different way from the present invention, since the type of probe used is quite specialized in the disclosure of the last mentioned patent. It is also noted that the high side of the AC power mains is connected directly to the touch plate in this disclosure, which is viewed as being extremely dangerous practice.
U.S. Pat. Nos. 3,770,981 to Nelsen and 4,002,923 to Larson et al show integrators for shaping an input signal which is later used as a control signal. In U.S. Pat. No. 4,002,923 the system is operated by proximity to a touch plate, but it does not in turn operate a CMOS flip-flop which controls a silicon control switching device. U.S. Pat. No. 4,081,700 to Hamilton also shows the idea of controlling a flip-flop with a touch plate probe.
U.S. Pat. Nos. 3,200,304 to Atkins et al; 3,309,690 to Moffitt and 2,810,066 to Green show proximity controlled circuits wherein an oscillator is caused to oscillate when an approach is made to the probe.
In order to provide truly economical stand-by operation in which the current drawn is extremely small when the device is in the OFF state, it is necessary not only to use CMOS circuitry, but it is also necessary to use it in such a way that it can be biased at or near its most economical current drawing levels, i.e. biasing the individual CMOS chips off from their center voltage levels where they draw the most current. Moreover, it is necessary to protect the CMOS circuitry against excessive voltage inputs which will destroy the CMOS chips. Finally, in order to achieve a circuit which has at the same time a high degree of sensitivity, and a low false alarm rate, it is necessary to provide a highly stable circuit in which a great deal of wave shaping takes place so that upon the approach of a body to the probe the power switching circuit receives a definite control signal free of meaningless spikes and free of unwanted reversals in the rate of change of the control voltage toggling the circuit from one stable state to the other stable state.